Fischer Carbene Complexes of Iridium(I) for Application in Catalytic Transfer Hydrogenation

Abstract

New examples of the very rare class of iridium­(I) Fischer carbene complexes (FCCs) are reported from the facile transmetalation from group 6 FCCs. Postcomplexation modification of either the carbene ligand or the ancillary coligands results in a tunable IrI metal center, for unprecedented application as a (pre)­catalyst in a benchmark transfer hydrogenation reaction. The introduction of an aminocarbene ligand with a pendant N-donor moiety capable of hemilabile coordination yielded the best catalytic results with turnover frequencies reaching 445 h–1 and requiring 0.1 mol % catalyst and 0.5 mol % base loading, respectively.

Carboxamide carbonyl-ruthenium(ii) complexes: detailed structural and mechanistic studies in the transfer hydrogenation of ketones

“…To fully understand the effect of the base in the TH of ketones, we carried out a number of control experiments. First, an experiment using KOH base alone without the ruthenium complex was conducted and afforded percentage conversions of 5% (6 h) and 16% within 36 h (Table 2, entries 1 and 2) and are consistent with the findings reported by Polshettiwar et al 43,44 This is much lower compared to the percentage conversions of 86% (6 h) reported using the Ru3/ KOH system (Table 2, entry 9), thus confirming that the catalytic activities observed are due to the Ru( ii ) carboxamide complexes. In another control experiment, we used complexes Ru3 and Ru4 without adding any base.…”

Catalytic Deoxygenation of Nitroarenes Mediated by High-Valent Molybdenum(VI)–NHC Complexes

“…While traditional methods such as direct hydrogenation − or transfer hydrogenation have been intensively explored in this area, these methods still have some major draw backs, as the need for precious metal catalysts, ,− complicated (chemo-)­selectivity strategies, − or the need for pressurized reactors, which are not commonly available in all laboratories, as well as the need for potentially hazardous hydrogen gas . Although the latter can be overcome by using transfer hydrogenation processes − ,− with different hydrogen delivering reagents, e.g., isopropanol or silanes, these protocols often require a large excess of hydrogen suppliers and may create large amounts of (hazardous) waste byproducts. ,− In this context, oxygen atom transfer reactions (OATR, Scheme )­ hold great promise, not only because of their high atom efficiency − but also due to simple executions and the need for cheap, earth-abundant early transition metals. − Furthermore, OAT reactions focus only on oxygen containing functional groups, which makes them ideal candidates for chemoselective reductions compared to “classical” hydrogenation reactions.…”

Transition-metal acyclic carbene complexes: building blocks for luminescent, stimuli-responsive, bioactive materials and catalysts

“…Highly active catalytic transfer hydrogenation of acetophenone using the Ir( i ) acyclic carbene complexes has also been reported. 103 Their catalytic performances in terms of product yield and TOF with 0.1 mol% catalytic loading are superior to those of related complexes with cyclic carbene ligands.…”

“…18) have also been reported to catalyze addition reactions of aldehydes and ketones (Scheme 6). 102,103 A series of Rh(I) acyclic carbene complexes can efficiently catalyze the addition of aryl boronic acids to benzaldehydes with an yield up to 96%. 102 The enantioselectivity of the catalysis can be improved by modification of the substituents of the carbene ligands (Table S4, ESI †).…”